IN-403 Silver Creek Bridge

Information and Findings From DHPA Historic Bridge Survey

Statement of Significance

The IDH built a limited number of spans on its 200' Parker design. The structure appears to retain its original members, including the metal guardrails.

Architectural Description

Instead of modifying its standard design for 198' Parkers to accommodate decks wider than 25', the Indiana Department of Highways developed a new 200' model in 1939. In comparison with the old standard, the new one used nine instead of eleven panels, thus increasing panel width from 18' to 22'3", and heavier members.

The IDH combined the new design with its standard concrete substructure and coped and paneled approach rails. The single-span's top chords slope at different angles in each panel. The outer verticals consist of an I beam, and the others are made of laced channels. I beams also supply the outer and the center-panel diagonals and counters; laced channels compose the other diagonals. The lower chord members are crafted from a pair of channels riveted together with battens and stiffened in the center panel with an added plate. Substantial portals and cross-frames, arched to allow for more roadway clearance, brace the trusses. Riveted to the verticals at and above the lower chord, heavy I floor beams carry the 25'10" concrete roadway.

Other Information

A. G. Ryan and Sons of Evansville, Indiana, won a $60,780.74 contract in December 1940 to build one of the longest Parker through-truss spans of state design upon concrete abutments. The new structure was probably completed near the end of 1941. The ISHC had developed standard plan #1521 for a 200-ft. span with a 26-ft. roadway sandwiched between a pair of 2-ft. walks. Truss depth varied from 24 ft. at the portal to 39 ft. at midspan. Each truss carried nine panels, the outer two on each end at 20 ft. 7.5 in. and the inner five at 23 ft. 6 in. Every top chord member is differently sloped; only the central panel's one is parallel with the lower chord; and all were fabricated from a pair of 15-in. channels (@45# for the endposts, third, fourth, and fifth panels, and @40# for the second). For the lower chord, a pair of 15-in. channels riveted together with battens grow in weight from the outer panels (@40#) to the inner-most one (@55#). The state used rolled I-beams in a few web members. The verticals or posts consist of two forms and weights: the hip vertical is a 10-in. I-beam (@33#); the others are made from a pair of laced 10-in. channels (@15.3#). To protect the quite-tall trusses against wind and vehicle-induced stress, substantial latticed struts and heavy upper sway framing buttress the verticals above 15 ft. of roadway clearance. The portals used latticed sections, too. While a 10-in. I-beam (@41#) provided the second-panel diagonal, the third used a pair of laced 10-in. channels (@20#), the fourth a pair of 12-in. channels (@23.7#), and the fifth a 10-in. I-beam (@21#). Only the central panel was countered. The ISHC prescribed 30-in. I floor-beams increasing in weight toward midspan (@172#>200#) riveted to the verticals above the lower chord. Eight rows of rolled I-beam stringers attached to the floor-beams' sides varied in depth and weight by placement. The 20-ft. panels used 16-in. Is at 36 lbs. for the outside and 18-in. ones at 55 lbs. for the central ones. The 23-ft. 6-in. panels relied on 16-in. outer Is at 37 lbs and 21-in. Is at 29 lbs for the inner ones. Together, the floor-beams and the stringers carry the concrete deck. Angles supply each lower sway-bracing member. Tube-channel-and-post rails lined the inner sides of the trusses, and coped concrete approach rails with bush-hammered panels funneled traffic into the spans.

This bridge illustrates the state's longest standard trussed span. The trusses retain their original members. The metal guardrails and the concrete approaches also remain. When the concrete deck was replaced, so were a couple of the stringers.

1975: Concrete Deck and Stringers Replaced [SHPO database]

Bridge Considered Historic By Survey: Yes